Semialdehydes, ketoacids, and their esters contain an aldehyde or keto group, respectively, in addition to a carboxylic acid or a carboxylic ester group. Reaction of a diol with the aldehyde of a semialdehyde leads to acetal formation, while reaction of the keto group of a ketoacid leads to ketal formation. Diols having a 1,2 hydroxyl group configuration (such as 1,2-ethane diol (ethylene glycol)) will form a dioxolane and diols having a 1,3 hydroxyl group configuration (such as 1,3 propanediol (propylene glycol)) will form a dioxane group. Higher polyols, such as triols and tetrols, including polymeric polyols, can be used to form cyclic ketals as well when at least two of the polyol hydroxyl groups are in the 1,2 or 1,3 configuration.
Acetalization and ketalization is generally carried out in the presence of an acid catalyst, for example a homogeneous, protic acid catalyst such as sulfuric acid, hydrochloric acid, phosphoric acid, p-toluenesulfonic acid and the like.